1. Field of the Invention
The present invention relates to a mobile communication system, and more particularly, to a smart antenna receiver in a CDMA (Code Division Multiple Access) communication system and a signal receiving method therefor.
2. Description of the Related Art
A smart antenna receiver using adaptive antenna array technology automatically adjusts an antenna to the optimal direction according to information obtained by receiving an input signal by respective elements.
As indicated in FIG. 1, a conventional smart antenna receiver is comprised of a multiplier circuit 110 including a plurality of multipliers 110-1, . . . , 110-n formed correspondingly to an adaptive antenna array, a summer 120, and an adaptive processor 130 for adjusting adaptive weights.
In operation, array input vector signals X1, . . . Xn received from a plurality of antennas of an adaptive array are respectively applied to the multipliers 110-1, . . . , 110-n where they are multiplied by weights W1, . . . ,Wn of complex numbers adaptively adjusted by the adaptive processor 130. The output signals generated from the multipliers 110-1, . . . , 110-n are supplied to the summer 120 where they are summed up to generate an array output y. Thus, in a receiving beam pattern, gain is increased in the direction that a desired signal is received and a null is formed in the direction that an interference signal is received, so that a signal can be spatially selectively received. Therefore, the circuit shown in FIG. 1 is called a spatial filter. The spatial filter increases the capacity of a system by reducing the interference between the same channels in a CDMA mobile communication system.
The adaptive processor 130 for adjusting the adaptive weights of the conventional antenna receiver adjusts the adaptive weights W1, . . . , Wn only by the array input vector signals X1, . . . , Xn and the array output y. The adaptive processor 130 carries out complicated calculation processes including searching for the direction of a signal source by calculating an optimal weight, obtaining an autocorrelation matrix of a received vector signal, and obtaining an inverse matrix and a unique vector of the autocorrelation matrix.
Therefore, it takes long periods of time for the adaptive processor to process the calculations. In addition, the circuit of the adaptive processor is complicated. Consequently, it is difficult to apply the conventional smart antenna system to the CDMA mobile communication system. The reason for the complicated circuitry of the adaptive processor is because the information about the difference between the desired signal and the interference signal is not fully used.
It is therefore an object of the present invention to provide a receiving apparatus for simplifying calculation processes carried out by an adaptive processor by using a pilot signal in a CDMA mobile communication system.
It is another object of the present invention to provide a signal receiving method for simplifying calculation processes carried out by an adaptive processor by using a pilot signal in a CDMA mobile communication system.
According to an aspect of the present invention, a smart antenna receiver using a pilot signal in a base station of a CDMA mobile communication system, comprises: a plurality of multipliers for multiplying radio signals received respectively through a plurality of antennas by adaptive weights; a summer for generating an array output signal by summing outputs of the plurality of multipliers. The smart antenna receiver further includes a pseudo noise code generator for generating a pseudo noise code which is detected from the pilot signal and has been used in a transmitter; and a first multiplier for generating a despread signal by multiplying the array output signal by the pseudo noise code. A data bandwidth filter eliminates an interference component by filtering the despread signal and a limiter adjusts an amplitude of the interference component eliminated signal. Additionally, the smart antenna receiver includes a second multiplier for generating a re-spread reference signal by multiplying the amplitude adjusted signal by the pseudo noise code; a subtracter for generating an error signal by calculating the difference between the reference signal and the array output signal; and an adaptive processor for generating an optimal adaptive weight using the error signal and the radio signals.
According to another aspect of the present invention, a signal receiving method using a pilot signal in a CDMA mobile communication system using a smart antenna receiver, comprises the steps of: multiplying radio signals received respectively through a plurality of antennas by adaptive weights and summing the multiplied signals, to generate an array output signal. The signal receiving method further comprises the steps of: multiplying the array output signal by a pseudo noise code detected from the pilot signal to generate a despread signal; filtering the despread signal; adjusting an amplitude of the filtered signal; multiplying the amplitude adjusted signal by the pseudo noise code to generate a reference signal; calculating the difference between the reference signal and the array output signal to generate an error signal; and generating an optimal adaptive weight using the error signal and the radio signals.